docs: document when and how tests are run (OSPS-QA-06.02) (#79)

Adds two sentences to the Testing section of README.md explicitly
stating that tests run automatically on every PR and push to main, and
lists the other checks the workflow runs (npm audit, OSV scan,
type-check). Satisfies OSPS-QA-06.02 which requires documentation of
both when and how tests are run.

Generated with Claude Code

Signed-off-by: Paradoxbound <paradoxbound@users.noreply.github.com>
Co-authored-by: Paradoxbound <paradoxbound@users.noreply.github.com>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: paradoxbound

README.md

@@ -225,7 +225,9 @@ npm test
 
 ### Testing
 
-Functional tests run against a live BookStack instance. Set these environment variables:
+Tests run automatically on every pull request and every push to `main` via the [Functional Tests](https://github.com/paradoxbound/bookstack-mcp/actions/workflows/functional-tests.yml) GitHub Actions workflow. The workflow also runs `npm audit`, OSV dependency scanning, and a TypeScript type-check on every run.
+
+To run tests locally, provide credentials for a live BookStack instance:
 
 ```env
 TEST_BOOKSTACK_URL=https://your-test-bookstack.com